As one of the major components in soil ecosystem, soil enzyme plays important roles in converting soil nutrient, improving soil fertility and remediating pollutant in soil. This study focused on long term monitoring enzyme activities of three hydrolytic enzyme (urease, invertase, alkaline phosphatase) from fixed sites at fertile land to establish a more realistic index of total soil enzyme activity. The result showed that there is a good correlation between soil enzyme activity and soil fertility. Correlations between soil enzyme activities and characteristics of the soil are significantly or very significantly positive. This suggests that enzyme activities of urease, invertase and alkaline phosphatase in soil environment could be used as an indicator for soil fertility. A new total soil enzyme activity index from this study ( E_t=∑Xi/X) was proposed which is a dimensionless parameter and could be used to compare with each soil samples easily. The E_t can be calculated from monitoring enzyme activity in soil and soil fertility, as the result of total soil enzyme is similar to those of principal component analysis (PCA) and clustering analysis.